Department of Biosciences, Molecular Cell Biology of Plants, Goethe University, Max von Laue Str. 9, 60438, Frankfurt am Main, Germany.
Department of Physics, Syracuse University, 201 Physics Bldg., Syracuse, New York, NY, 13244-1130, USA.
Plant Cell Environ. 2017 Aug;40(8):1643-1657. doi: 10.1111/pce.12973. Epub 2017 Jun 2.
Glycerolipid synthesis in plants is coordinated between plastids and the endoplasmic reticulum (ER). A central step within the glycerolipid synthesis is the transport of phosphatidic acid from ER to chloroplasts. The chloroplast outer envelope protein TGD4 belongs to the LptD family conserved in bacteria and plants and selectively binds and may transport phosphatidic acid. We describe a second LptD-family protein in A. thaliana (atLPTD1; At2g44640) characterized by a barrel domain with an amino-acid signature typical for cyanobacterial LptDs. It forms a cation selective channel in vitro with a diameter of about 9 Å. atLPTD1 levels are induced under phosphate starvation. Plants expressing an RNAi construct against atLPTD1 show a growth phenotype under normal conditions. Expressing the RNAi against atLPTD1 in the tgd4-1 background renders the plants more sensitive to light stress or phosphate limitation than the individual mutants. Moreover, lipid analysis revealed that digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol levels remain constant in the RNAi mutants under phosphate starvation, while these two lipids are enhanced in wild-type. Based on our results, we propose a function of atLPTD1 in the transport of lipids from ER to chloroplast under phosphate starvation, which is combinatory with the function of TGD4.
植物中的甘油脂质合成在质体和内质网 (ER) 之间协调。甘油脂质合成的一个中心步骤是将磷酸脂从 ER 运输到叶绿体。叶绿体外膜蛋白 TGD4 属于细菌和植物中保守的 LptD 家族，特异性结合并可能运输磷酸脂。我们描述了拟南芥中的第二种 LptD 家族蛋白（atLPTD1；At2g44640），其特征是具有桶状结构域，具有典型的蓝细菌 LptD 的氨基酸特征。它在体外形成具有约 9Å 直径的阳离子选择性通道。在磷酸盐饥饿下，atLPTD1 水平被诱导。在正常条件下，表达针对 atLPTD1 的 RNAi 构建体的植物表现出生长表型。在 tgd4-1 背景下表达针对 atLPTD1 的 RNAi 使植物对光胁迫或磷酸盐限制比单个突变体更敏感。此外，脂质分析表明，在磷酸盐饥饿下，RNAi 突变体中的二半乳糖基二酰基甘油和磺基奎诺糖基二酰基甘油水平保持不变，而在野生型中这些脂质增强。基于我们的结果，我们提出了在磷酸盐饥饿下 atLPTD1 在 ER 到叶绿体的脂质运输中的作用，这与 TGD4 的作用相结合。
